The present invention relates generally to the field of scanners and other devices used for transforming an optical image of a document into an electronic signal and more particularly to a flat panel illuminator active transparency adapter for a scanner.
Electronic document scanners, copiers, and facsimile machines transform an optical image of a document, photograph or transparency into an electronic signal suitable for storing, displaying, printing, processing by a computer or electronic transmission. A document scanner may be a separate device or a document scanner may be a part of a copier, part of a facsimile machine or part of a multipurpose device. For opaque documents, reflective scanners typically have a controlled light source which is reflected off of the surface of a document, through an optics system, and onto an array of photosensitive devices. The photosensitive devices convert received light intensity into an electronic signal. Transparency scanners pass light through a transparent image, for example a photographic positive slide, through an optics system, and then onto an array of photosensitive devices.
A transparent image may be scanned in a reflective scanner by placing a white surface behind the transparency. In such an arrangement, light passes through the transparency to the white background, reflects off the white background and passes through the transparency a second time before impinging onto the photosensitive devices. Therefore, light is filtered twice by the transparent image. In general, this double filtering creates an unacceptable distortion of gray scale, color, contrast and other image characteristics of interest.
Reflective document scanners may be adapted to scan transparent images by providing a separate light source to back-light the image so that the light passes through the transparency only once. In some systems, separate mirrors, lens and other optics may be required to properly project the image onto the photosensitive devices. Motors may also be required to move the external light source relative to the image. One such method is to use cathode florescent light bulbs in the scanner lid, so that there is back lighting, rather than reflective lighting for scanning transparencies. This method creates a very large scanner lid, since the florescent light bulbs are typically xc2xd to 1 xc2xd inches thick. This is also expensive in terms of additional components and requires a complex power supply to ensure that all of the lights are stable and the same brightness throughout the scanning process.
U.S. Pat. No. 5,463,217 (Sobol et al.), which is incorporated herein for all that it teaches and describes, describes a completely passive adapter for scanning transparent images in a reflective scanner without requiring a separate light source for back lighting. A light source in the reflective scanner provides light which passes outside the area of the transparent image. The adapter captures the light which passes outside the area of the transparent image and reflects the light through the transparent image. The reflected light re-enters the scanner along the optical path required by the scanner internal optics. The various embodiments described in Sobol et al. are suitable for a fixed scanner optical path. However, when a new scanner is developed, the angle of the adapted mirrors may need to change to accommodate a different optical path within the new scanner. The adapter of Sobol et al. requires an arrangement of mirrors, metal or a folded metallic coated cardboard adapter to be placed onto the platen glass. The adapter of Sobol et al. comprises at least one additional component to the scanner that may be misplaced or damaged. A similar transparency adapter is disclosed in U.S. Ser. No. 09/127,454 U.S. Pat. No. 6,018,161, entitled Adjustable Adapter for Scanning Transparencies with a Reflective Document Scanner by Patrick Batten et al., filed Jul. 31, 1998, which is also incorporated herein for all that is taught and disclosed. Neither of these methods permits a full size image to be scanned when a transparency is being scanned.
Another method in which reflective scanners have been adapted to scan transparent images by providing a light source and moveable mirrors in the lid of the scanner. U.S. Pat. No. 5,710,425 (McConica et al.), which is incorporated herein for all that it teaches and describes, describes a scanner with a light source and moveable mirrors in the lid of the scanner and two different light paths depending on whether the document to be scanned is opaque or transparent. The first light path would reflect off of an opaque document and the second would pass through a transparent document. The mirrors within the lid reflect light back into the base of the scanner or onto the document being scanned. The device of McConica et al. require many components to be installed within the lid of the scanner and also require two separate sets of optical components to support two different light paths. There are also moving parts within the lid, which may get out of alignment due to opening and closing of the lid as would be required under normal scanner use.
It would be desirable to have a scanner transparency adapter that is integral with the scanner, but does not add significantly to the component count or cost of the scanner, does not add significantly to the manufacturing cost, does not add significantly to the overall height, size or weight of the scanner, does not add moving parts to the lid of the scanner that may get out of alignment due to mechanical jarring accompanied by constant opening and closing of the lid, and does not significantly increase the complexity of the scanner or the power supply of the scanner.
The above and other aspects of the present invention are accomplished in a scanner that utilizes a flat panel illuminator in the scanner lid in order to provide back lighting when a transparency is being scanned. A scanner according to the present invention will enable the scanner and transparency adapter to be an integral unit that is smaller and less expensive in terms of manufacturing and component costs than the transparency adapters of the prior art. Also, the transparency adapter will have a less complex power supply and will consume less power than the cathode florescent light bulb, backlit transparency adapters of the prior art. The flat panel illuminator of the present invention may also be slid or snapped into the scanner lid so that the end user may simply install the flat panel illuminator into the scanner lid when a transparency is to be scanned. One alternative is to have the scanner base light turned off whenever the flat panel illuminator is lit. Another alternative is for the flat panel illuminator to be unattached and separate from the scanner, such that it can be placed over a transparent document when needed and either plugged into the scanner or a different power source during the scanning process.